It could actually suggest that there are two Silent Hill games in production...

One by Kojima... one by Del Toro... one 1st person, one third person, two separate products that could be taking the episodic nature of MGSV (Ground Zeroes / Phantom Pain) A prologue and a main chapter? Two different games with a common connecting theme? Maybe one shorter Downloadable and one full length retail? Maybe they're both included in the same package and both Kojima and Del Toro are crafting two separate but overlapping experiences?

Kojima has discussed looking at game development in an episodic nature to get games out faster... And this is one thing he's tried with MGSV already. Who knows?

They so are gonna add canon story. I feel they will explain a lot of what always made the franchise mysterious .

I seriously hope they do not try to explain too much and ruin the mystery, also it's not really their place to explain too much of the big stuff, it's like if they were changing the name of the town (even just adding 1 letter) it would be too much of a liberty.

From what I saw in the teaser, I have two possible theories, one "horizontal" and one "vertical".

HORIZONTAL THEORY: There are a near-infinite number of parallel universes, each a little different. When you're passing through that door, you're transported to a different reality, just a little different from the last, even if the difference is only a time one. In one reality, things might be "normal", in another, the lights are red, in another there's that freaky thing in the sink, etc.

VERTICAL THEORY: I've often theorized that Silent Hill is kind of like an elevator shaft connecting our world and hell itself (or the devs' interpretation thereof). As you go from room to room, you are descending lower and lower, which is why things seem to get more nightmarish the further along you go.